Circuits for object locator apparatus



R F MOZLEY 2,613,317

cmcuns FOR OBJECT LOCATOR APPARATUS '7 Sheets-Sheet 1 INVENTOR ROBERT FMQZLEY flww ATTORNEY Oct. 7, 1952 Original Filed April 12, 1943 Oct. 7, 1952 R. F. MOZLEY 2,613,317 CIRCUITS FOR OBJECT LOCATOR APPARATUS Original Filed April 12, 1943 I 7 Sheets-Sheet 2 HOLLOII PIPE /O/ONNECTIONS ELECTRIC gff COMPUTER MODULATOR 'sm Vcos \/34 A J /-5O 47 RADIUS RECEIVER TO TIME DELAY DEMODULATOR CONVERTER 2' mmcA'roR sh H As WIDE TRIGGER GATE PULSE AWORNEY Oct. 7, 1952 F. MOZLEY 2,513,317

CIRCUITS FOR OBJECT LOCATOR APPARATUS Original Filed April 12, 1943 7 Sheets-Sheet 3 87 y 2i J9! -89 *1}; a

cos-N p COS-M ix x cos-L h Y G FIG. 8.

I b v INVENTOR DIHEDRAL 5 ROBERT E MOZLEY 1952 R. F. MOZLEY 2,613,317

CIRCUITS FOR OBJECT LOCATOR APPARATUS Original Filed April 12, 1943 '7 Sheets-Sheet 4 DISTORTING AMPLIFIERS MULTIPLIER DEMODULATOR r-IIS I F l G I 5.

\NVENTOR ROBERT E MOZLEY ATTORNEY VFIGV. l4.

Oct; 7, 1952 Original Filed R. F. MOZLEY 7 Sheets-Sheet 5 DRIVING moioa AND HOLLOW PIPE couusc'nous MOVING GATE ILL-5| TRIGGER 4s 45 P RECEIVER gQ INDICATOR A u z a 4ss7a9 F I e I? iNVENTOR ROBERT EMOZLY ATTORNEY R. F. MOZLEY CIRCUITS FOR OBJECT LOCATOR APPARATUS Oct. 7, 1952 7 Sheets-Sheet 6 Original Filed April 12, 1943 5mm] u I INVENTOR F ROBERT E MOZLEY 2 #0417 1 ATTORNEY Oct. 7, 1952 MQZLEY 2,613,317

CIRCUITS FOR OBJECT LOCATOR' APPARATUS Original Filed April 12, 1943 7 Sheets-Sheet v {we TRANSMITTER TRIGGER A I99 TRANSMITTED PqLsE .WIDE GATE -a'r 89L i2 88 Moms GATE as 9| F D J20: E FIRST RANGE GAT SEcoNo RANGE GATE GROUND SIGNAL \J 208 lNPu-r To PEAK VOLTMETE'RS PEAK VOLTAGE OUTPUT INVENTOR HQ. E9. IPOBERTE/W02LEY ATTQRNEY V in between the aircraft carrying the locating Patented Oct. 7, 19 52 Robert Mozley, Berkeley, Calif assignori The Sperry Corporation, a corporationof De omoorrs v ware j Original application April 12, 1943,-Serial "No. i 482,807, nbwlPatent No. 2,495,753, dated Jahu, ary 31,1950. Divided and this applicationAugust 27, 1949, Serial No. 112,666 i This invention relates generally to aeronautical object locator apparatus and has reference more particularly to novel circuits useful in such apparatus where it is desired to locate objects without interference from ground reflections. This application is a division. of Patent No. 2A951753 granted January 31, 1950.

An objectof the invention is to provide novel circuits for object locator apparatus such that objects between an airplane and the ground are detected and located without interference from the ground itself, the said circuits also being suitable for detecting objects projecting upwardly from the ground such as high buildings and other obstructions.

It is another object of my invention to provide object or target locator apparatus circuits for computing the products of sinusoidal functions or products of functions of various angles.

It is also an object of the invention to provide circuits for simulating cosecant and secjant curves in response to sineand cosine indications.

It is a further object to provide circuits for object locator apparatus for producing amoving gate responsive to the distanceof the aircraft to ground.

Other objects and advantageswill become apparent as the description proceeds.

In certain types of radio locating or searching systems, what is known as type-C indication is employed. This signifies that a target or object which is to be detected from an aircraft, for example, is located by scanning with a radio beam which is caused to traverse a spiral course In such apparatus anindicating device, such as a cathode ray oscilloscope, is provided in which a cathode ray beam is also caused to. move spirally and to produce an indication on the screen of the cathode ray tube in case a target is intercepted by the scanning radio beam. This type of apparatus has the merit that the position of the target in both azimuth and elevation is indicated upon a single screen. I

However, if the aircraft carrying the locating equipment is flying low or the distance range of the locator is greater than the altitude of the aircraft, the scanning radio beam will thus intersect the ground for a considerable solid angle of the angular range of the cathode ray oscilloscope indicator. Reflections from the ground will take place throughout the'area of the screen corresponding to the portion of the solid angle of the scanning system subtended by the ground plane. In the event that a target should come 9 Claims. (Cl. 250-27) f 2 equipment. and ground, such a' target be obliterated by the ground reflections.

' It is accordingly an object of my invention to provided methods, and apparatus for enabling targets to be located anywhere Within the angular range of locating equipmentqregardless of the height at which the searching aircraft is flying or the relationship of the target to the ground plane.-

Other and further objects will become apparent as the description proceeds. V i

In carrying out my invention in its preferred forms I- provide attachmentsfor radio beam scanning apparatus forascertaining the distance to ground and controllingthe receiver of the scanning apparatus to eliminate ground reflection whenever the scannenisso oriented that the distance to ground alongthe. radio beam is less than the'normal linear or radial distance range of the apparatus. l i

In accordance with one embodiment of my invention, the distance to ground along the radio beam axis at anyinstant is computed electrically from the altitude 'of the aircraft andthe instantaneous angles ofthe radio beamof't-he searching apparatus. Mechanism'is providedfor reducing the radial range of the locator to a distance slightly less than the computed distance to ground. For example, means may be provided for producinga square Wave voltage having a' time duration varying in accordance with the computed distance to" ground. The indicator is provided with a voltage control for making the indicator eiiective only when the control is energized. The squarefwave, having a time dura tion corresponding. to computed distance to ground, is applied to the voltage control of the indicator so that when'fthe searching beam is directed toward the groundthe indicator remains effective only for a duratioriof time less than that required for a transmitted signal to travel a distance equalling the distance to ground along the radio beam axis and return along the same path to the radio locator. Inthis manner, any

target between the aircraft and ground produces is liable to A better' understanding of the invention will Jbe afforded by the following detailed description a considered inconnection' with the accompanyin drawings, and .those features of .the invention I which are believed to be-novel andpatntablewill bepointed out in .the'claims app-ended hereto.

In the drawings, U I Fig. 1 is a view offlthe. screen of an indicator ,9; fora type-of radio locator 'systemin'whichiiny' invention may be employed.

' Fig. 21s a perspective view .of thegroundplane and of an aircraft shownfwithin .ahypothetical hemisphere having a radius equalling the maxi- .mum range of a radio locator installed on the air-7 craft, the sphere .being cut'by the groundiplane.

' Fig. 3 is a schematic diagram of 'a radio-loca- Fig. .'5 is a. schematic diagram ofa modification inthe arrangements illustrated'inFigs. Band .4 which may be employed ffor electrical 'multiplication of angular indications. H v V Fig. 6 is a circuit diagram of a devicefor pro- 'ducing a time delay or gate length proportional to a voltage, which is inturn proportional to the distance to ground along the'axi's of thescanner ofa radio locator. I v

Fig. '7 is a graph representing the gate produced. by the apparatus ofFig; 6. I v

Figs. 8 to'"12, inclusive,=are-perspective views of three dimensional diagrams, Fig. 8 being a diagram showing-a ground plane-in relation to a system of rectilinear coordinates, Figs. 9 and 10 "being diagrams of "spherical'p'yramids drawn to illustrate the manner of mathema'ticallydetermining the relationship between itheirectilinear coordinates of Fig. 8 and spherical coordinates, 'Fig. 'll'being a 'diagram in which the representations of Figs;- 8," 9 and 10 have been simplified and co'mbi'ne'd 'to'form a: single diagram and .Fig. l1 2"being' adiagram illustrating the conversion :of rectilinear to spherical coordinates.

1 Eig..13 is:a circuit diagram'of :amodification tin a :portion ofithe apparatuslofl ig. 3.

I i. Fig .14 .is .a -graph-.-:of a secant curve .repre- .zsenting One .factor of @a computation .used in the i-apparatusofliigrii. H 1 I Fig. 1-5 is agraph of anelectrical-functionsim- -ulating thev curve oiFig. 1.4..

Fig. =16 is a schematic diagram .of a radio 10- ,cator receiving ,systemcorresponding to the apv ..paratus .of Fig. :3 .but employing automatic elec- .trical means of. measuring distanceto ground instead of employing means forcomputing such a .distancetoground I 1 Fig. 17 is a schematic diagram illustrating the .principleinvolved .in electrically automatically changing the range inaccordance with distance a General. explanation. of .z'llustrative locator system For the r-sake-of illustration, I shall :describea .manneriof carrying out my invention in :connection with a spiral-sweep pulsed-microwaveradio- .1

beam scanner of' the type represented schematically in Figs. 3 and 16. In this type of radio locator or searching scanner there is a radiator .II- comprising a parabolicrefiector .I2, with a 5 ,jparabola' zaxis [:3; and. having ai'dipo le zantenna (notvisibl'e in the drawings) mounted at the -focus of the parabola I2. The radiator serves both for the purpose of projecting a radio beam inipulsesiotirnicrowave oscillations; and for the ',';re.c.eption of any pulses which may be reflected V I ,in ase the beam is intercepted by a target or an 'obstacle to aviation. The parabola axis I3 is also the radio-beamaxis.

Suchja systemis illustrated and desc ribed in greaterrlietailiin,thacopending application Serial I No."-z441;1-88,;filed.April 30, 1942, by White, H01- 'schuh, Mieher and Shepherd. It-will be under- -stood, however,"that my invention is not limited to .useWith a spiral spinner scanner or with the ingsfandthe description of the present .application.

In this type 'o'f' radio 10am the radiator II is soniouritedas to be'rotatable about a-spin-axis',

so that the beam I3 tends "to describe a cone. The radiator is alsopivoted about-an axis I5 transverse 1 to the spin-axis "l l and'whi'ch rotates with -the shaft 2 II. The pivotaxis I 5 may be" referred'to as a=nOdaxisl "Nodmotion of the radio beam lfl causesthe apex angle of'the conedescribed thereby to'bhange progressively to "produce-a. spiral sweep. For-pivotally supporting H the radiator 'I l,-a' yoke' l S -n'i-aybemounted on the shaft I4 and the radiator parabola II may-be m'ounted 'one 'T*meniber -I'I whichhas" trunnions supportedby the yoke 'Ifif The members I4, [6 and '-l="l-a're in th-e form of hollo-w pipes actingas a jointed wave-guide typed-transmission line .for

40 transmittingmicrowave radio energy to and from the radiatonli. w

The radio scanner, together with associated apparatus which will be described'more in' detail hereinafter, iisfmounted on an: airplane I'8, "shown 5 in Fig; "2. 'In' Fig. -2 "there is sh'own a hemi sphere I9 described by'a radius of length R, which is the maximum radial range of 'the'r-adio scanner. Since it is impracticableforthe-nod motion "or rotation of the radiator I I about the nod axis I5 ,5 to be made greater 'than-'90-in most installations,

"the maximum-solid-angle which-may be assumed to bescannedbythe radiator I I 'is'tliehemisphere l9"shownin"Fig.2. Means are provided for 'rotating'the" shaft 14 carrying the radiator I I to'produce a-spinning moti0n,'and means'lnot shown) are also' provided for rotating the-radiator I I; about theaxis I 5 to-produce anod motion. 'The nod-motion is made relatively slow in comparison-with the spin motion so that theradio beam axis I3 describes-a spiral on the surface of the hemisphere I9. 7 The projection of this spiral trace-on a plane circle is represented in.Fig." 1, which also represents the trace of the cathode ray; beam of an-indicator which is-used in con- 165 nection with the radio locator apparatus. "Such an indicator may comprise a cathode ray v.tube having a screen ZI. The spiral trace is represented by the curve 22in Fig. 1. 1

In=radio locator apparatus of the spiral "sweep 270 type, means are ordinarily provide'd for preventingthe cathode ray beam of the'indicator-from striking the screen 2| unless a target is inter- :cepted by the radio beam 'travellingalong the caxis I 3. Aspiral trace :22 ,shown in Fig. 1, .there- Time 'dfles ctu ly appear. on: the screen .21

specific type of radio locator described in said apv plication, and schematically represented by drawrepresented in Fig. '3 I by a supporting 's'haft I4,

screen 2| and the angular position of the spot 23,

as wellas its radialdistance from the center 24 of the' screen 2|, serves as an indication of the position of the target in azimuth-and elevation with respect to the airplane It. It will be understood that the screen 2! is provided with suitable calibrations soas to relate the indications thereon to the azimuth and elevation angles of the radio beam axis i3 intercepted by a target 23 Fig. 2). V In the event that the altitude h at which the 'pl'an'e' lii is flying is less than the radio range R of the radio locator equipment, the hemisphere 19 will have the lower portion thereof intersected b'ya plane 25, representing the ground plane or surface of the ground. Under this condition the lower'segment 260i the indicator screen 21, corresponding. to the solid angle subtended by ground plane '25, will produce reflections for any position of the radio beam axis'ld in which the beam "axis 113 strikes the ground. Accordingly, the segment 25 of the indicator screen 2 i will apparently be covered with target indications, which may be referred to as ground targets or ground reflections. In the event that some obstacle to aviation or a hostile airplane should be. present l along a line drawn from the airplane 8 to a-pcint 20 on the ground, the indication of such a target on theindicatcr screen 2! is liable to be obliterated by the mass of ground reflections 28.

For the purpose of overcoming difficulty from ground reflections, -I eliminate such reflections from the screen 21 by reducing the radial distance range of the radio locator equipment from the maximumvalue R to shorter range values while the radiator! l is in such angular positions that the radiobeam' axis It strikes the ground.

; The problem of eliminating surface reflections arises when an aircraft is flying over bodies of water as well as when flying over land masses, and l-employ the term ground inthe description and claims to refer to the surface of such bodiesof water as well as to theearths land surface. a

Q Computer type ground reflection eliminator For eliminating ground reflections in the type of apparatus illustrated in Fig. 3, the radial distance r to ground is computed from the angular positions of the radiator ii and the'altitude of the airplane, and the range of the radio locator apparatus is automatically reduced in accordance with the computed distance to ground. In order to obtain continuous indications of theangular positionsof the radiator II for the computation of radial distance to ground, suitable angular position indicators are provided. Preferably reinoteposition indicators are employed in order to simplify. the construction. For example, I may utilize a transmitter 26 of the type used in conventional electrical angle transmission systems,

after, the stator 21 may also be so mounted as to be adjustable in angular position.

For transmitting indications of nod angle, a similar angle transmitting system Imayi-be provided comprising a transmitter 3i with a stator tzhaving a rotor (not visible'in Fig- 3) secured to a shaft 33 whichissecured to the member I! directly supporting the radiator ll. As in the case of the stator 21, the stator 32 may also be so mounted as to be'adjustable in angular position, for reasons which will be explainedhere inafter. 1 r

Suitable means are provided for continuously computing the radialdistance'to ground in terms of altitude and the angular indications provided by the transmitters 2 G and 31. For example, an electric computer 34 may beprovided having one input connection in the form of a pair" of electrical conductors 35 from the spin angle trans! mitter 25, and a second input connection in the electrical indication proportional to altitude.

Apparatus suitable for this purpose is shown and described in U. S. Patent Re. 21,955, November 25,1941, to'J. G. Chaffee. The apparatus 38 has an output connection through apair of con ductors tawhich serve asa third input connection for the computer 34.

It will be understood that microwave pulse radio locator apparatus of the type illustrated includes a radio receiver Al and an indicator 42 havingthe screen 2| on which the indications of the presence of a target appear. Such a re clever has an input connection, ordinarily in the form. of a rectangular hollow pipe wave-guide 33, leading from the radiator II. In the schematic drawing there is shown a box -44 which'is assumed to contain a driving motor for rotating the shaft l4,as well. as suitable hollow pipe connections for transmitting to the pipe #3 radio frequency energy received through the hollow shaft, It. In such systems also a suitable transmitter (notvisible in the drawing) is provided for trans mitting pulses from the radiator H and associated with the apparatus there is also a trigger pulse source (not shown) for synchronizing'the transmitter and the receiver 4!. Such a trigger pulse sourceis arranged for synchronizing a wide gate supplied to'a receiver connection ltlaf-ter the termination of the transmitted pulses, for

rendering the receiver responsive onlyto reflectedsignals. A suitable connection 45 isprovided from the receiver 4! "to the indicator 42 for produoingindications when reflections are received by the receiver 4|.

The indicator Q2, however, is also provided with a control connection, represented by'a pair of conductors 47, for eifectively reducing the range of the target responsive apparatus comprising the receiver 4! and the indicator 42 in accordance with signals supplied to the control connection 41. Although the apparatus. is shown as having the control connection M applied to the indicator i2, it will be understood that the arrangement may also be such that the control connection is applied to the receiver 4!, or to some other suitable portion of 'theapparatus."

In the specific embodiment of the apparatus illustrated, the effective distance range of the target responsive apparatus is controlled by con,-

trolling the length of the interval of time during which the apparatus'is effective. To this end,

means responsive to the output of the computer 34 aiiezprovideti -for:producing a i-variable-length voltage-lgateatonsquare wave "which is applied to the ;input fconhection' -41 of the indicator -42. such meanssmay take the form of an electronic circuit): designated as :aradius-to --time-delay conrei' ter; represented in Fig.3 by a rectangle 48.

- Fen-reasons which will be explained hereinafter,

45, and there :is-a: pair of-conductors 52 servingas anwdutput connection from the demodulator 49 and aninput connection to the radius-to-timedelayconverterfl. The device 48 may alsohave' ,a-ptrigger pulse connection represented by a pair of conductors for synchronizing. it with the pulse-transmitter (not shown) which also synv chronizes the Wide gate '45 of the receiver 4|.

, l-=A1thQugh my invention is notlimited to a particular method of mounting the radio locator apparatus, the electrical computation of radial distance-to ground'may be simplified, and accordingly a simpler form -of electrical computer #34 maybe employed, if the equipment is so mounted-,or the aircraft carrying it is so flown, that ithcishaft l4 remains horizontal, and some reference axis transverse to, the shaft l4 also remains horizontal. For-example, the equipment maybe mounted on a platform maintained horizonta ,1 by suitable gyrosc'o'pic;controls, or the radiator ll maybe mounted in the nose of :an

c'eiver-il ands58. .:It will be understood -that'zthe transmitter 51 has a rotor secured to-the gyro fore andaft shaft 55, :and the receiver 58 -has,=a rotor mechanically connected throughgearing'lil to the spin axis angle,transmitter-stator :26 for adjusting'rthe position of the stator 26 to -compensa'te for-roll of the aircraft or of the platform on which the radio locator may be mounted. It will also be understood that :suchself-sym chronous systems are provided with 2118011113601,

single-phase exciting current 62 through pairsof conductors 63-leading to both-the transmitter and receiver.

A similar self-synchronous transmission -sys- I tem for compensating the angular indicationof the nod axis is provided comprising a Selsyn' transmitter 64 'witha rotor secure to thezgyr'oscope axis 56, a receiver, 65 with a :rotor mechanically connected by gearing 66 to the angular transmitter stator :32, and conductors 6.1 joining the transmitter Bland the receiverffii. .Thesame source of exciting current 62, supplied through conductors-Gamay bezprovided for the transmit;-

ters 64and receiver 65.

. Although other structural arrangementsmay be utilized, for the'sake of simplicity in thedrawings, the nod angle transmission devicesf3luand 65 have been shown as moving with the yoke I6 and therefore necessarilysupported by suitable members secured to the shaft 33. This would necessitate the useof sliprings, orthelike (not shown) forcarrying the electrical connections through the conductors '31, '61, etc. Itwillbeunderstood that in practice the transmitter 3! may be connectedto the means (not-shown) for rotatinglthe radiator H about, the nod axis 15.

The transmitters 26 and 3| may, if desired, be of the type sold as Telegon transmittersrep resented schematicallyrin Fig. 4. ln such apparatus there'is a stationary exciting winding 68 "arranged for magnetizing an axially .-ex t'ending magnetic rotor-69 with transverse'projection's H.

aircraft with the axis of the shaft I4 along the fore and aft :line of the fuselage, and the aircraft may; be flown level whenever the indicator 42 is to be observed. However, to avoid necessity for maintaining-theapparatus in a predetermined levelplane, whether itis-mounted directly onthe aircraft or on 'a.;platform movable with respect to the aircraft, :I may'also pr'ovide suitable-meansfor compensation of variations in the reference. points for. spin "and nod angle -from ".fixed references which" would exist for level fiying-conditions. Tothisend, the stator 21 of the spin-angle transmitter 26 ismade adjustable in angularjpcsition, and-likewise, the-stator 32 of the nod angle transmitter '3 I z 1 I For adjusting the angular-positions of the sta 'tors' 2-1. and ,32 to predetermined reference positions, a gyro'system'53 may be provided comprisinga schematicallyrepresented gyroscope 54 with argimbal shaft 55 parallel to the axis of the spin- -ner driving shaft 14, anda perpendicular shaft -56 which remains horizontal by'virtue of the actio ;of'thezgyroscope 54,w-hich maintains its axis vertical.- -Angular transmission systems are pro vided for adjusting the angular positions of the stators 32 and2'l in accordance with relative angular positioned the gyroscope shafts-55and 56.

For adjusting the angular position of the stator 21, a self-synchronous angular transmission system, suchtas a Selsyn system for example,

may beprovi'ded comprising a Selsyn transmitter 51 and -aSelsyn--receiver'58 with polyphase {conductors ,59"joininglthe transmitter and re- There is a stator-comprising a pair of crossed pickup windings 12 and 13 arranged -at right angles to one another and havin magnetic axes perpendicular to each other and to the axispf the rotor shaft 28. For use in my apparatus, the windings 12 and I3 are mounted on the'a'ngularly adjustable stator frame 21 which may have a shaft 14 secured'thereto connected tothe gearing 6| of Fi .3.

' .For ius'e, with the type of computer;.3 4,}'described for the sakeof illustration'in the present application, only one: of the stator windings 12 and 13 need be 'employed, or,-if desired, the stator windings 12 and 13 may-be connected in series to the output conductors 35 or 31. Alternating voltage'having the same frequency as the source supplied to the exciting winding '68 is induced in the pickup windings 12 and 13. The arrange- 'ment is such that as the rotor 69 rotates with the shaft 28, thealternating-voltages varyin' peak value-0r are-modulated, a thesineor, cosine of the angle, according to the reference point taken.

The apparatus 38 may comprise a known form of altimeter such as thatshown and described. in the above-mentioned .Rei'ssue Patent" 21,955, measuring vertical distance to ground (not shown) with :a: source of; alternating current :and

means driven v by therraltimeter :for: varying the amplitude of the alternating: current. in accordance with thealtimeter-indication. in this manner, the device.v 36 produces a "modulated alternating voltage fluctuating in peak-"value in ac-'- cordance with: the; altitude indication; "Thefalti- 59; tude indication is therefore of the same type as that provided by the transmitters 26 and 3|.

The computer, maybeof the type described in the copending application of Herbert Harris, Jr.. Serial No. 474,052, filed January 28, 1943, now U. S. Patent No. 2,497,883 dated February 21, 1950, in which an output is produced proportional to. a product orquotient of the amplitudes or envelopes of several modulated input alternating currents or voltages. -The radius-to-time-delay converter 48 may comprise a pair of electric valves, such as vacuum minimum value of the graph of Fig. '7. As repre sentedby the double arrow 92 in Fig. '7, the portion! of the graph may be moved to the right or to the left by varying the magnitude of the voltage supplied between the radius terminals 52.

Since the computer 34 continuously computes the radial distance to ground, that is, the distance along the radio beam axis [3, the time the tube 76 by a condenser 85' and positively biased by means of a resistor 86 connected to a point at positive potential, for example, to the positive terminal of the anode supply source 81. For adjusting the tubes to the proper portions of their characteristic curves a bias source '15 may be provided for the tube 16. e v i The circuit of Fig. 6 is designed to produce a square wave 81, as illustrated in Fig. 7, having a fixed amplitude and having atime duration tdependent upon the voltage applied between the radius voltage input terminals 52. In Fig. 7 the voltage amplitude of the square wave is plotted vertically and time is plotted in a horizontal direction.

Since the control electrode 85 ofthe tube H is positively biased, the tube I! normally conducts current, a large voltage drop takes place in the load resistor 19,.and the voltage between the gate output terminals 41,. is aminimum, as represented by the portion 88 of the graph of Fig. '7.v When the circuit is triggered by a trigger pulse applied to the terminalsi5'l, which also triggers the transmitter..(not shown) and the delayed wide gate 45 of the receiver 4|, the tube 76 becomes conducting ,driving the control electrode 85 of the tube 71.. negative, so that the yoltage output of the tube "l'i appearing between the gate terminals 4'! abruptly rises along the line 89 in the graph of Fig. '7. i

The tube 16 remains conducting for a period of time depending upon. the magnitude of the radius voltage supplied between the terminals 52. Thus, the voltage applied at the radius voltage terminals 52 serves as a variable bias for the tube 16. I After the'trigger pulse has died away the current flow through the tube 16 is determined by the grid bias, which in turn depends uponv the magnitude of the voltage applied at the radius terminals 52,. ,Thisjzcurrent flows through the cathode resistor 80. and therebycontrols the cathode bias of thetube'l'i. The greater the voltage at the terminals 52, the greater the potential of the cathode ofthe tube H and therefore the greater the length of time required for the coupling condenser flfi to discharge sufficiently for the potential of the control electrode 85 to rise to cutoff and again render thetube Tl conducting. When the tube 17 becomes conducting; the output voltage across the gate terammy again falls along the u e 9i to the duration of the portion 81 of the graph in Fig. 7 represents the distance to ground. The indicator i2has a control gate applied to its control terminals 47; which permits the indicator to be effective only for a time duration fixed by the length ofthe control gate. The adjustment of the rece ver ll and the indicator 42 is such that the time required for a signal to be transmitted the distance represented by the length of the control gate Bl is slightly greater than the actual time duration of the gate 81.

Consequently, if any target or obstacle should appear at a point-93, Fig. 2, between ground and the airplane it, an indication thereof will appear upon the screen 2| of the indicator 42. However, ar'ter the time interval required for a transmitted wave to reach ground and the reflected Wave to traverse the entire distance r (Fig. 2) from a point on the ground back to the airplane IS, the indicator will have become unresponsiveand no ground target indication or ground reflection will be produced on the indicator screen 2|. a h

. Operation in general The operation of the apparatus of Fig. 3 as a Whole is brieflyas follows when level night is assumed. Withrespect to the aircraft supporting the radio locator, the radiator or scanner H executes a spiral motion causing the beam [3 to sweep a solid angle of space which may be a complete hemisphere. If any target intercepts the beam 13, a bright spot 23 appears on the screen 2l (Fig. 1) in a position corresponding to that of the target. However, the computer 34, responsive to spin angle, nod angle, and altitude continuously computes the distance to ground along the beam [3 and reduces the radial distance range of the apparatus to a value just under the radial distance to ground whenever the beaml3 points'toward the ground plane 25 (Fig. 2); In' this manner ground reflections are avoided? For the case when the spinner shaft It is horizontal and there is no pitch or roll of the support for the scanner, the computer 34 may be arranged to solve the equation:

CSO S 9 where r is the radius or length of the beam [3 fromthe scanner H to the intersection of the beam with ground plane 2,5, 1,0 is the nod angle;

and 0 is the, spin angle, The nod angle 0 is measured from the spin axis, the axis of the spin shaft 14, and the spin angle 9 is measured from areference point vertically below the shaft l4, which is assumed to be horizontal for this case.

The angle 11/ never exceeds in practice and tive and may be caused to assume a suitable scram computer to be-capable of producing an indication of-'a computed result greaterthan- R.

- In casethe assumed level condition-nolonger exists and the support for the locationapparatus-rolls, i. e., rotatesaroundthe axis oi -the spinning shaft l4, the-efiectof roll is-fu-lly compensated by-correction the spin angle -9 by adjustment of thestator' 21.; by meansot the. gyroscope system 53. Provided pitchdoes'not become excessive; it is substantially compensated by-correction f-- the nod -angle b' by adjustment ofthe'stator- 3'2 by means of the gyroscope system 5 3.

" In -;case the spinner shaft M isnot assumed to be normally horizontal, a more complex solution for -r-isqrequired and the" principle involved may best be understood by a mathematical *analysis;

For the sake of simplifying the construction, I- have referred to the}po'ssibility of making a certain simplification the computation of radial distance to-grounmand I- have referred to the possibility-of mounting the apparatus-in a particular manner with respect to theaircraft to simplify the --computati'on. However; my invention is not limited to the mounting-arrangement specifically "suggested; The principle in- PlYfid e came lia-hon r. a ial. is e. to r d. wil h. r iQ e.-.firsi e. x lained. 101: he ener l. ase. Where he radio. pcatqr pa tus. s; mquntedn-v an de ire position arelati n o. a airc ett eel-the; .11 m. tins; par tus here ors ree assume a gular osi. .Qn w h fifi ect t he; qr o The. eneth.. oi he radius? al e. hwadia am 3. s; e a ertained/1% erms. i:- he ircreit. lt ude... h and. e: an ular; ce dieates i;- he; direction; at that?tam;-v

Computation o;- dis-tance -toground;

7 E heeener les he grou d. Pl ne. may be assum to fq l l e wit reagent e ny. et of ocr ne T e; r n i nvolv d; W lli;

. better, understood, by. considering the equation of he r und lane 215. n. sp eri l r inates about P asanorigin. I The equationpfthe ground plane-I art sian orv re t l e r oor i ates;

where h is the -alti tude of aircraft and-therefore the length of a normal Pei from the origin P to the ground plane 25, and L, M and N are the direction cosines ofwthe normal" PG with respect to-the X' X; Y'Y: and-Z':Z axes shown in-FigL-t.

' The projection of the linePG on-the-XY plane issa-lon-g a. line PA shownin Fig. 11. [A- plane I through- PAG includes. the ZZax-is and-is per- .pendicular to the XYr-plane Referring-to Rig. 9; and applyingthetheorems 0f...spherica1. trigonometry, sincethe dihedral 90. Eq ation. limar the iberewr tten bysubst-itutine va u sifrcm; eu.ati ns i oii .1 he equations. for he r und: n ane.- .eti -1 the roun p ane; u tion n; pherical; were nat sisaoh a nedir:

,(i ii he Z2 {axis 18 ssumed he. he. pin a is through the shaft. la rthefscanner the spin a es: an h pdtan l e sq i d: r

haZfZ. ax s n tead. o .fr m Y. p ns is.

' '"cos 'b cjos' fgi sin tease-F v os 'x in. '9 i Wa n. nJ c M The angles b and. were the angles niathe scanner supporting.- frame: workv with. resliecti t0 the ground plane 25; Since the gyroscope. 5.4 maintains a level; thaangles b and amay; be obtained also fromthe. gyroscope; For-ta very general-casein which the supporte ing framework ofhtheiscanner is free tozvary in angular relationship to the ground plane; the computer 34' may be supplied with angular; in;-

puts from thegyro' transmitters. 64.. and Well asthe spin and nod angle transmitters 26 and 3|, and thealtimeter=38n In this case the computer. 34: is. designed to solve Equation .12

above; It is unnecessary, however; for thecome puter 34 to be capable OfCOmPIItiIlg VaILIQSwf'I greater'than .R, the maximum possible range of-the radio locator -equipment. .t

If lthe aircraft. is. assumed. to be '.'so ;fiown that the spinaxis remains parallel to the ground, WhIChYiS usually the case forv :gundire'ctor =systems, the. angle. b1 isuzero'. If themaircraitis This simplifies. the apparatus required. .to .iorm the computer 34.

f he. spin axi escanner spam s the foreand aft line of. the aircraft, 'rolljotthe craft is fully compensated; by correction'or'the duced.

Modified computation The electric computer 34 has been represented as being so designed as to divide a variable voltage by the product of two othervariable voltages. In order to obviate. the necessity for utilizing a computer capable. of handling two separate input quantities inthedenominator, I may provide means for multiplying the voltages cosine a and sine u supplied by the inductor pairs 35 and 37 before the voltages enter the computer. For example, I may utilize an electro-dynamic voltage multiplying system.

, As illustrated in Fig. 5,.the voltages induced in the stators 2i and 32 of the angle transmitters and 3! may be multiplied by utilizing a cascade connection. One of the transmitters, for example the transmitter SL'may have a rotor magnetizin winding ficenergized by the source of exciting current 63, and a pick-off winding 96. Itwill be understood that the pick-oh winding 96 is connected by means of ashaft 9'? or the like to the gearing 66, shown in Fig. 3, to maintain the stator in the proper angular adjustment with respect to the horizontal.

i The other angle transmitter, in this case the transmitter 26, has its rotor exciting winding 68 connected to the pick-off winding 96 of the transmitter 3i. The'rotor of the transmitter 53! rotates with the shaft 33 according to the nod angle of the radiator H and the rotor 69 of the transmitter 26' is driven by the shaft 28 according to the spin angle of the radiator ii. The voltage induced in the pick-off winding 9% has the frequency of the excitation source 53 and is proportional to the product of the voltage of the input source 63, which is constant, and the sine of the. angular position of the rotor shaft '33. A sinusoidally modulated current is utilized for. magnetizing the rotor 69 of the transmitter 26. Accordingly, a voltage is induced in its pick-01f winding 12 which has the frequency of the excitation source 63, but has a peak value or amplitude proportional to the product of the sine of theJ-angular position of the shaft-33 and the cosine 'of the angular position of the shaft 28.

It'willbe understood that the angular reference points are so chosen that the' function is the sine function in one case and the cosine function in the other case. i

' The voltage appearing in the pick-01f windings 72 may be supplied to a suitable quotient computer as'a divisor. It will be understood that a voltagemodulated in accordance with the altitude will also be supplied to the computer so that the result is the quotient of the altitude voltage and the voltage supplied by the cascaded transmitters 3| and 26 of Fig. 5. i

If desired, necessity for the use of-a quotient computer may be eliminated by converting the v voltages supplied by the transmitters 3i and 28 into a quantity varying as the reciprocalofthe product, or two separate voltages proportional to the cosecant and the secant of the nodangle and-:= the spinaangle, respectively, may be pro- For the purpose of not'cnlyproducing such a- I reciprocal voltage or voltages, but also producing a voltage or voltages of constant maximum amplitude for theangles which would have negative values of the secant or the cosecant, I may utilize a distorted amplifier circuit such as shown in Fig. 13, for example.

In the arrangementof Fig. 13, demodulators 03, 02 and W3 are provided for converting the modulations of the carrier voltages between the conductor pairs 3?, 35 and 39, respectively, into fluctuating voltages representing the envelopes with. the carrier (excitation) frequencies removed. For converting the output voltages from demodulators ill! and I03 into voltages representing the secant and the cosecant, respectively, distorting amplifiers I04 and are provided. These-may be electric valves of the vacuum tube type, forexample, such as pentodes having control electrode or grid circuits connected to the outputs of the demodulators llll and I03, respectively, and having load circuits with output connections m6 and H11, respectively, serving as input connections to a schematically represented multiplier circuit W8. It will be understood that such pentodes also have screen grids: and suppressor grids. r

The altitude demodulator I02 may have an output connection comprising a pair of conductors 509 serving as an input connection to the multiplying circuit Hi8, which may thereforebe arranged to multiply directly three. fluctuating unidirectional voltages supplied by the connections Hi6, iil'i and N39 to give a unidirectional output voltage. Such an output voltage is supplied to a pair of conductors 52 serving as an input connection to the radius-toetime-delay converter 48 shown in Fig. 3.

The distorting amplifiers I04 and liltiare similar in arrangement and principle of operation and therefore only one of them need be described in detail. I'he amplifier lfl l has a load resistor l i 9 connected in series with its anode lead to the positive terminal of an-anode supply source H2.

The anode voltage is supplied to the multiplying circuit ce through the connection we, and the output of thedemodulator it)! is applied to the control electrode through a pair of conductors H3. If necessary, the demodulator iiii may include an amplifier for supplying to the tube [M a voltage of sufiicient magnitude to enable the amplifier EM to distort the input voltage. For biasing the tube M4 at the point at which increasing values of input voltage produce successively greater degrees of saturation, a bias voltage source I i l of suitable voltage is provided.

Referring to Fig. 14, representing a secant curve plotted against angle, it will be observed that the portions of the curve in a region near zero and are relatively flat as compared with a cosine curve which has a relatively sharppeak. Likewise, the portions of the curve in the region near 99 and 2701degreesare very steep as compared with-the slope of a cosine curve near 90 and 270 degrees. Furthermore, the slopes at all points are reversed as compared with the slopes of a cosine curve. The reversal of slope is pro duced by a vacuum tube amplifier which is resistance coupled to the output because such an amplifier acts as a phase inverter.

The flattening of the curve near zero degrees and the steepening of the. slopenear 90 degrees and 270 degrees is accomplished by the distorting characteristic of the amplifier I04.

Although my invention is not limited to theuse of anyparticular class of electric valves or vacuum tubesi theirequiredi characteristicsimay be obtained abythe use of: tubes having relatively sharpcut off and having theinplate voltage versus 'plate curvescrowded more closelyv together to the zero -by-its. curve-.= For example; pentode vacuum tubes may be used of the 6A0? or the 6SJ7 type. I

v When utilizing tubes of this type :referring :to the tube: I84- shown-in Fig; 1-3; the load resistor I I I preferablyhas a resistance-greater: than that. w-hichcprovides the g-reatest degree of linearityf the-load characteristieflor example; twoor. three timesthe resistance for -maximum linearity. I In order to:.obtain the desired distorting characteristics ion increasing :voltage inputs it is desirable to havetheload- 1inch oi thetuhe; drawn on the plate current-plate voltage curve lessjn slope' than the load -line whichprovides maximum linearity; This" is accomplished utilizing: relatively high-load resistance -It-z will-be recalled that-whenthe radia-tor II with reterence to Edgy-8; is in the angular a positions betwcen=90=andi270 degrees," the radio been I 3'--is pointing upwards and the computed values of distance to A ground have no significance because the beam I 3 n'ever-strikesthe:ground; I The distorting amplifier I04 provides a eonstant'oute put VoItage I r' -the l values of R- between 90' and 2-70 degrees becauseduring-these angles the value oi cosine-becomes:negative'so thatthecontrol I electrode :ofthe tube-I 04k is simply driven-.imore negative; The value-of the biassource I is such that the tube I 04 -is--biased slightly beyond cutoff and-therefore th'output voltage for zero input and slightly -higher. is equal tothe voltage of the supply sourced-I Accordingly, negativeinput voltages-have no further effect-and between I, 90 and 2'70 degrees theoutput-voltageremains asa constant value,- the-voltage of the-source: I I2 as represented by-the'iine I I 5-in Fig; 15;

Inasmuch as -thesecant"curveinFig. 14 becomes infinite in value in the-regions I near 90 and I 270 degrees; corresponding to values of the cosine maximum rangeltof the locator" apparatus. In this manner the:comp-uter'serves-tosupplya control voltage -to the indicator 42 which reduces the efiectiverange; of the receiverandf-indicator when the-radio beam--I3-i s pointed toward the g-munmt has-no effect-When the radio beamis pointed upwards; or-makess-ucha small angle with the groundthat the distance to ground exceeds themaximum range of the apparatus.

' h apparatus;- 5

It will be apparent that except for displace I mentin phase/the amplifier Ifliwill produce a curve having the sameshape as the output curve o-f 't-he amplifier" I84: As shownin Fig; 13; the

output wave-shape- I'I 6*of amplifienlfil simulates beam I3;- is; measuredelectricailyh Such a inithisroasc, isthcn is-tance o round.

16 system L185 represented: schematicallygirrifig. 'I'heitstructure 1 0i the. scanner; equipmentiillusgtrated is. similar to that. representedschemati example-itzmay bewappliedztoazchannelzinlthe receiver. Al: or tom-heindicator;has in-thc:-:at--.- raneement-;of;1=ie:13.; For sunplyinersuch amewin gatezto. moving 7 gateterminals 4:1, 311 morin c gate generator Ila-kiss provided. which1;.is: ;re+ spQnsivetotarget 'ran ewmeasurements obtained: from: the receiver: 41;, througha: connection I I 9.: In; effect:.the;apparatus:,of: Fig; 16: utilizes'the lance measurementaprodnced;by the; receivcn 4-I.

whenever the -radio: beam; I3.:strikes-itheground; 1

in order to roduce a moyinggate'hayinaa lengthcorresnonding tovthelran eameasurementwhich.

I As illustrated in tie-itwhcre-the mam; represents the maxim m cannin anslezor cone ithc r diator- H with a counterolo hwisezdirew onrof. spin and-withithe ma: radial .;r nee. of h app atus, as soon-as th radio. beamrhas been; u d s ffi -iently- 110% aa commas lone-:ras h max m meffeetive flIlECLSWiKQS. .thez round at a-point A ancithe receiver. pr duces/a ran e: measurem nt "r0. as 'th zradiatorall continuescto rotate. the measured uecshecomesmoeressivelyt short r, as epresentedby t e radii {I ,-;2-, 3; stamp to not wh h is he; minimum; v he orrespond-r g to th n sition' ftthezmdiatorg llqwithzthe m-- I3 in i s lowerm sttpositio i As-thereon tor II on in es o pin,.;the:ero11 d; rane iinses again:until he heamstrikes the poin s";- after which .zaaheam, as l n time maximumaetf st v l een n e s r kes earround; and: there is no f-urthen need ion liminatin round" reflection. It will Joe understoodthat:the1'radi.us' r0 orthejc r le I 2 -representsythemaximumvmnee For p ducinsa: movin igatezcontinuoiislyv portional to; the: varying :va'luesmf r,'measured by the receiver. 41. asuitahh circuitcsuchzasiazvaauumtube circuit mayibeiemployed-i Sacha-seize cuitisillustratedinvFig.'18; I

Ground distancefmeasurement j f he gwave.,pr ducedrthereby; a irangereate: sen:

erator. 23, m ans for aup ingz thdranem ete generator I23 to the square wavmgenerato ylzzg which c upling means.- aytake;theiiormior a uffer "or a d -t f llowerstage-J24, :.for-:exam-; p a s c nd.- r h czgatew enerator: I251: synchmn z d w t e output therfirstrmnsezeatezsene or I 3, a pair of coin iden e; devices 2 l 26 and a .p ir o lowrtimewc nstant peairwvoltmeters I28 and l a pain fwinte ratorsi I3 I and Imat -w d h iting diode; ke :biaszadiustinz device I 34' with;v arfeed-bechxconneetiomISitosthe square-wave: nera-ton I22:;.and; a constant-1cm;- rent device- I 36-: associatedgwith; therbias :atiiuste inc device: I34;

The, diu bleqsquare:waveeeherator Iflimar take; the form of" annuals-pulse z'multivibrator. circuit. comprising: await-of electric;v valvea: such as triode vacuum tubes I31 and I38, for exams ple, The tubes I31 and I38 haveconventional load resistors I39 and MI respectively, and have acommon cathode-resistor I42 Ifor coupling the tube I31 to the tube I38. For coupling the tube I38 to the tube I31, resistance-capacity coupling is employed comprising a coupling condenser I43 and a grid lead resistor I44 connected between the control grid of the tube I38 andthe positive terminal of a source of anode voltage supply I45 forpositively biasing the tube I38. I

"The initial tube I 3T-has a control electrode or grid I48,Icapacity coupled toIthe trigger-pulse input terminals and alsoconnected through a grid resistor I41 tQIthe conductor I providing albias potential. I 3 I The square wave generator .I 22 is designed to have the outputsquare wave appear at an output terminal I48 which is electricallyconnected to the anode 'off'the' 'tube I38. The output terminal I48 may be connected or "coupled to the indicator control con minals4'I. I I I,

The cathode-follower stageI24 may take the 'ections or moving gate teri'orm of a triode vacuum tube having a'control grid coupled to the output terminal "I48 of the square wave generator I22 through a coupling condenser I49 and a grid resistor I5I. f 'f The cathode-follower stag-e I24 includes] a cathode resistor I521 with 'a coupling by means of a'peaking condenser"l53 to, the first range gate generator: I23 for synchronizing the latter with the termination orjdescending potential portion of thesqua're wave appearing at the square wave output'terminal148. Thecapacitylof the conprjoduce the peaking actiom,

denser, I53 is maderelatively small in order to "Therange' gate generatorI23fmay take the form of a blocking oscillator comprising an electric' valve such as a triodejvacuum tube I54, for example, having a pair of transformer primary windings I55 andl55feach .connectedin series withthe anode'leadfto the anode supply source I45. ln'inductive "relationito the transformer winding I55 is a transformer winding I51 conjnected at :oneendjto the negative terminal of the supply source I through" "a grid resistor I58 and connctedat. the other end through a condenser I59. A junctionfterminm IBI of the "winding I 5'! and there sistor I58 is'connected to the controljgrid I62 of'the triode"I54;' In inductive relation to the transformerprimar-y winding I56is a secondary winding I 53 across which a potentiometer resistor I64 "may be connected. "Associated with; the potentiometer resistor I64 is a movable tap I forflproviding an adjustable amplitudeI output voltage which "will be in the form of a square wave byyirtue'of the k own characteristics lator circuit I23. I I

The second range gate "gt:ie rator I25"-is wi l,

pled tothe first rangegate generator I23 through a. differentiating or peaking circuit including a" condenser 1 I 65' for. synchronizing the generator t r 2I Th'secondrange gate generator I25 may also 5 with the end of the output wave of the gen- 'be in the form of. avblocking oscillator having elements and connections which are similar to of the blocking f oscil- I those described X in connection j with I the mage gate generator I23; A: potentiometer including a" movable brush I6! is providedior supplying an adjustable amplitude square wave'foutput. I

' The coincidence devices I26 and: I2'l-are double -input electric control'devic and may take the form ofvacuum tubes; so arranged asto havetwo. -'input=orcontrol connections each. Thus each I .1 I tub ould be ,atflea t ar etrddd th. p ircf ntr l. el ctro es. r, eridSII I. As shown hQWeY I the tubes M MZ] a e n hcicrm; o h me: grid co nverters having conventional pairs of shield gridsand conventional I suppre sor grids. The tu "Elia a: fi t c ntr-cl el t de 9 rid 168 up d I n- Isuita le man er; as y means of a oupuns condens ,I IaH I-aer leak resistor III, tojtheout'put terminal lfil gof t e seco d range sa ener or lI;2I5.I- l Sim: ilar manner, the tube I21 I has I a Ifirst; Icontrol electrode or grid 1 12; resistance-tapacity I-pou pled to the output terminaljfifili ofthefirst range gate generator I23. ;'I {he tubes IZG and I 2;] also have second 5 control electrodes or I signal grids I13 and I I14, respectively, separately resistancecapaci y coupled to an; input connectionI II9 fromthe receiver 4|} Fig.;l6) -I I fhe connection H9 is the one at which lthe r e ceiver; IIIIIsupplies what is customarily known asthe video output, which will bethe groundIsignal incase thera dio beam axis I3 is pointed toward the ground. F su n anode-cat ode; Icurrc t t the tubes,;l26 and J2? il -parallel a source o directional volt ge 115.;may beprovidcd- :Puls ran or er re provided witnp rvwmdi s 16 a l; n: s ies. w hzt e anode; onned.- tions of the tubes I26 and 'II2I, respectivelm In inductive relation I to the} 'transformer, I windings .HB and ITI areIsecondarywindings; I18 and-I119, respectively,. and for, adjustment of 'the rnagnijtude of the pulse I output, I potentiometei's I havin output taps IBI-I- andI I82 are provided; I Thesecf ondary windings I18 and IfIS are -conHectedItO give output I voltage of, polarity; opposite Ito the anodes of the tubeIs I l2figgand lI2'| 1 1': II The tubes l 26 -and I 21; I are; preferably IOIfI; a type such as thosesold as-fiSA'? tubes in which driving either grid- 1.188 :or 11113 (in the case of tu zfilsb low arcu ofi p entialmexfinguishcs current irrespective of j I the *potentialrjof the other grid; It will-- be understood -II'that the shield grids are I maintained I at a :substantially fixed potential I and that theasuppresson grid of each tube is maintained; at cathode.aor ground potential. I I I The -lowI 1 timeI bh tan't eakvoltmetersIJIZB .andyIZSI maybe in tha form of electric gvalves such as triode vacuum. tubeshaving thei-r'rcontrol grids resistanceecapacityi coupiedI t'o the: output terminals ,IBI and, IB ZrIofgILtheI coincidence devices I26; and 121., respectivelyminorder to cause the; tubes 12 8, and .129 I to function I-as;.peak

yoltmeters on pulse wideners; to v spread; the=, wave, condensers I83 and I84, respectively, are connested; between the cathodes; of the-gtubes "128 land I29 and the I negative terminalzofi the sup- I condensers I83 and I84,,tre spectively; JIhewtime o a ts pillha Icir uitsa fiic: nd I .4; I 35 are, sochosen that -the condensers I 83=andI II84 discharge' within a time, fduration of. the order :sof magnitudei of jtheiqpulse repetition I. rate (of, "the j pulse? system: with which. the; app ratus is "P1037661; 11 T I I Eon; establishing *a: biasing I potential for square "wave generator I 22 'tvhich} will depart fromthe average "value in accordancefwith the relative magnitudes of -the voltages measured by the-devices I28 and I I29,; 'the intgrat and' -I'32 are provided and they a e i er es" They may "take the id of electric control I devicesor electric valves such as triode I, "xstantifwith' respect to: the potential 1 1431, the constant current device I 3 6* is connected -inaseries withtheicathode lead of 'the tube I34 and for adjustment of bias, as previouslyz'rex- .1,-pleined;;the potentiometer I10, [801 is. connected amass-*2 119 vacuum tubes 'lia-vm-g "control electrodes or rids resistance capacity coupled to the cathodes or output connections .of the peak voltmeter tubes I28 and -IZIL'reSpecti'Vely. The tube- ISZ-is negatively biased and the tube I3I is adjustabl'y biased by means'of'a potentiometertap IID cooperating With a series resistor "I80" connected between the-deVices -I'M'and 'I3'6 v The junctio terminal "Iii-I of the integrator tubes I3] and I32 -serves-as the bias'control potential output for the integrator circuit.

a For limiting "the i potential output and thereby limiting the gate width of the "circuit of Fig. 18, thejgate width limiter I33 is connected between the integrator output terminal I81 and a voltage divider terminal I88. The voltage divider terminal I-BB nay'be' the junction terminal of a pair of resistors I89 --and HI connected in s'erie's to the "supply source I. For-avoiding abi upt variations in the potential of the terini n'al" I '98,"-a by-pa'ss condenser'I92 may be connect d: across the resistor I9l. The gate limiter 133 may takethe form of anunsymmetricalcurrent conducting device, rec'tifier, d iode vacuum tube, or-the like.'- The limiter-"(I33 is connected with it's cathode a't*the" potentialdivider terminal m and its anodeat'the intgrator termina1 I8I."--- I h1though'the lievice's HI, "I32' have been referred-Ito as integrators for the sake of identinoationj'it will a beunderstood that inorder ito obtain fast action or the circuit, the arrange ment is' preferably such that excessive smoothing ao on or integration isnot obtained." To

this end the circuit constants are "so selected that the capacity loading onthe integrators I3I,

- Iis not-s c great as to slow dow nth'e action o h'e circuit. Distributed capacity m ay-tereliedumn "to {provide the requi's'ite degree. of integration If a separate condenser-I90 is employe'd ts capacity should be'relati'vely small;

I 611 011117 131-131 may be thought-ofas a "mixer tor' providing; a single-ended output from I two inputs rather than as an integrator inasmuch as li ttle integration is desired.

For supplying, the potential of the integrator Y butpu't' terminal 31 81 wine bias connection I35 I "terminal- 1 81 and the connection 135. The

nathode follower; "15343 is-' shown as coinprisinga :triod'e. vacuum tube with "a control electrode dif ect-lv connected tothe integrator "output' terr'ninal i For-Sc using the/circuit Quint ma rhaX-iinum I {ate in'dication' input signals I are -re-' I c'eiiredntmm=the receivei fl through the-connecgrater-tube I31", and maiintaiining" th bias conf the 1 point series between-the tubes! 34: and I96; ,Thetube S r may take; the dorm of a pentocle-havinga onventionali suppressor grid tiedto ground-and aving a screen grid; nk-connected; through {a pping'resistOr -IQS to the positive, terminal of 's upply'source, I15. However,.-th e control grid 91 h?"iii i ilfiis Pe fmin r ti clyi srque understoo'd 'th at inradiolocatorsysterns .ofthe 3 type to which reference isihetde herein, the 'trans{ mitter (not illustrated)" and the receiver 41 are synchronized in action by means of a triggering ator associatedj'with the "transmitter; Such a triggering pulse is represented .by the peaked wave IBIi'in Fi'gtlQA. "Such pulses are repeated at a suitable repetition rate which may equal 2,000 per'i co c e. 'g. in certain types of radio locator apparatus. In'response to each such mgger pulse I98, a pulse I99 asshown in Fig. 193

. i's'produced b'yfthe transmitten'flhe pulse I99 is actually in, the form ofa wave .train of high frequency microwaveoscillations, for examplefa train of 3000,'suc'h -oscillationsin the. case 0110 centimeter w'aves'fleach continuing 'for a;.-pu1se durat'ionoione, micro-second; The. pulse wave 7 jforxii,QIfSB therefore; actually represents theiip'ecti nee e clone or such. a, transmitted" pulse e ns'ist'ng. of; microwave iojscillations directed in 1a bearnj'hy theradiator I I along the beam axis I3. In such radio locator apparatus known means have. also been "providedj forproducing aso -called wide gate; which is afsquarej wave fof relatively long duration, as illustrated at 72104" in Ii'gQISC'. jIfhemeanslforbiovidin -such a wide gate 'are so de's'i'snedithat the gate begins afte'rj 'the termin'a 't'ion o'f v the transmitted. pulse and terminates well 40 Vbefore lthej production of a succeeding transm'tted pulse. .fTheggate '2'f0l 'is 's'uppliedt'o the receiverjd'i through the wide. gate telfmilflals fin "order to. 'der the "receiver 4] responsive only during the enmeshed between transmi ted ,pulses so that the-receivercah pickup only reflected pulses and will not be responsive; [to sdirb ilft'ransmi'ss'ion of energy iroxnthe.transmittedrpulselI 99; Such rec'ei e'r' s are customarily provided jfWith a secondeategmpur errninalreiierr'ed, to'as a narrowsgate.connection'for further limiting-the I tllfneftlurationlduring which the receiver i'sf jrer spons'ive in or'de'r to cau'se the apparatus to pick Elections 'fron only afpafticularftarget region,

theflaitter an: een ientla niovinglgate m the rdrmiliu stc I a at 202. min g giep spending ,7)

ng gate generator lI8',Fig.i6'), and u a Beferriiig Fig; l8 .lthe moving-gate is forined v the multivioratorfi 22 in the n iannen described 'th Fig. The vgate,lengthis pulse which is, ordinarily generated hy a gener is produced I by the I 21., conductor 135, which corresponds to the connection'52 of Fig. 6.. The termination of: the moving. gate 202, along the vertical descending line: 9| (Fig. 19D) trips the range gate generator I 23 and causes a relatively short time duration square wave orrange. gate 203 to be generated (Fig, 195.). Thetime duration of the square wave 203 is fixed, being determined by the circuit constants of the generator I23. In a similar mannenthetermination of the first range gate 203 tripsthe second range gate generator-l25 and causes the commencement of a second range gate 204 (Fig. 19F). The-range gates .203'13I1d 204 are displaced along the time axis but, are substantially contiguous, i. e.. oneibegins approximately when the'other ends. I

{A signal received by thereceiver II and sup! plied to the moving gate generator II8 through connections ;II9 has a waveform 205, as illustrated in Fig. 19G. For reasons which will be explained hereinafter, the form 205, which is a groundiisignal when thereceiver is receiving reflections from the ground, is caused to divide substantially equally between the time periods represented by the first and second range gates 203 and .204. I

Assuming that avariation hastaken place in the-distance, to-ground causing the ground signal 205 to occur earlier orlater than the assumed time of occurrence, all or a preponderant portion of the ground-signal 205 will occur during the time interval of one of the range gates .203 or204. Assuming, for example, that distance along the radio beam I3 to ground is decreasing, a preponderant portionof the ground signal 205 will take place duringthe time period of the range gate 203. In this case, the coincidence device I2 (Fig. 18) will have both of its control grids I12 and I14 energized simultaneously, the grid I14 being energized by the ground signal received from the connection IIS, and the grid I'I2 being energized by the output wave 203 of the pulse generator [23. f A relatively strong output pulse 206 will therefore be supplied to the peak voltmeter I29. The other coincidence device I25, however, will not be caused to carry current, or will carry only relativelylittle current, for the reason that although a ground signal is supplied to the screen grid [13' from the receiver connection 9 the control grid I58 will either not be energized at all during the continuance of the ground signal 205, or be energized for only a minute final fraction of the time duration of the ground signal 205-. Consequently, theintegrator tube I32 will have a greater input than the integrator tube 131, causing its impedance to fall thereby lowering the potential of the integrator output terminal I87. This in turn-causes the cathode follower I34 to increase its impedance, and to reduce thepotential of the feedback connection I 35, since current-is held constant'by the device I35 and its impedance falls'to holdthe current constant. This fall in potential lowers thebias ofthe square wave generator I22, causing the'length of the output wave tobe reduced.

Inasmuch as the peakvoltmeters I28 and I29 have sloping output wave forms, as illustrated ,inFig. 19I, a smooth-variation in the integrator output is obtained with variations in the portion connection I35 isprogressively variedin response to successive transmitted pulses and correspondirigsuccessive reflected ground signals so asqto, adjust .the'time duration of the moving ;gate 202 and'to causethe groundsignal .205 to. besplit with respectto the timeof occurrence between the :range gates 203and 204. 1 3

Variations, in, the distance to ground along the radio 1 beam axis I3 take place continuously whenever the beam is pointed. Itoward the ground. These are cyclical variations due to the spinning action of the scanner as illustrated by Fig. 17 The nod action also causes cyclical variation, Furthermor it ea t tches or if t,.. h n in a t tud v r o s ,r n adi l. dis ance *9 ground. The latter variations arewnot cyclical but are also continuous or progressive. The ay ing gate circuitof Fig.18 continuously followsall such variations and eliminates theground signal from the screen 2I of the indicator 42; Ref ferring to Fig.' v1'7, itwillbe seen that the gate length of the moving gate must be afmax'imurn h npthe beam rik h e' he can A, mustthen decrease progressively to represent decreasing distance to ground until the point E isreached, and then must'increase'toa maxi mum at the point B. Duringthetime interval requiredfor the beam to rotate from the "point B counterclockwise ,back to the point-A,"thegate length should remain amaximurn. The [drift resistor I93 (Fig.- 18) insures that fthe'apparatus will remain'at maximum. range in "readiness-for themoment when the bearn'strike's the ground at point A. The variations referred to arepro gressive and therefore 1 the gate 202' follows progressively to controlthe indicator 42. How ever,' if a target should be located, the signals reflected therefrom'will represent a discontinuity andwill notjafiect'the autoranging apparatus of Fig'. 18oz? the-moving gate 202. Theautomatic reduction of range to less than slant distance to 'grounda'long the beam axis takes place regard less of the typeof sca'n" employed. 7 f

It will be understood that the connection I I9 fro'm'flthe receiver must betaken from a pointin theereceiver circuits ahead of the point at which a moving gate control voltage is applied order tojleave the appropriate channel of the receiver 4I active long enough. to produce the ground signalj205j1t will be seen from Fig.- 19, however, that the'moving gate 202 is terminated before 'the occurrence of the'ground signal-205. Consequently, the ground signaldoes not appear in the portions of the receiverfollowing themoving gate connection, and doesnot appearin the indicator 42.

' ,If exceedingly rapid variations in theyrate or change of, distance ground are anticipated it maybe desirableto provide means to make the gain of theauto ranging circuitbecome greater with larger error, that'is, larger deviationbetween the position of'the ground, signal205; referring to Fig. 19G, and the position of the common sides of the range gates 203 and,204. This may be accomplished by'freforming the ground signal 205 so as to 'form a relatively triangular the range gate 204 along the dotted line 2II, as

shown in the Figs.,19E andlSF. Suitable circuits for effecting suchmodification in the shape of the rangegates may be employed. Although I- may modify the arrangement of the :range rgat'e generators @123 and 125 toeifect the desiredchange in shape of the range gates, for the sake .of 'si'mpllcity in the "drawing, Ihave indicated the means for effecting the chang in r'angewgates schematically by means of rectangles 2 152 and '2 [3 (Fig. 18') representin'g suitable wave shaping cire cuit'si i w "'Runwa y'approach control ""The limination of ground or surface reflec- 'tion's in accordance with my invention is valuable for increasing the effectiveness of object location regardles's'of thepurpose for which the object location equipment is primarily :used. For example; it is valuable for increasing the safety of 'aviatio'n by making object location equipment responsive to the "presence of otheriairc'raft or responsive "to stationary obstaclesljutting' upward from the ground. The elimination of ground re sect ons is particularly valuable, -ho'wever,"'fo'r certain purposes-such as traffic control-and run-'- wayfiapproach controlbecause 'in crowded airports, a large number of 'planes may desire to land at substantially the same time -during a fog or other, conditions when visibility is low and the pilotsmust resort to blind landinggor depend on directions from "airport control centers. In accordance with my invention, the trafiic control in y-fb'e "transferred from the airport to the airplane itself. Such contro'hwill be much more effective 'because the operator in an airport 'contr'dl center is aware only of the presence of airplanes which have communicated with the operator; whereas the "pilot of an airplane equipped hir'adijo object'location 'apparatusjhaving the gr "ndrefle'ctions eliminated in'ac'cordance with invention, has an jindicationupon his screen also of their exact orientation. Accordingly, in accordance with my invention, it is unnecessary for airplanes to land foneat a time awaiting instructions from an airport control center "and pilots mayjlain'd in "rapid succession after assurling themselves oftheabse'nce of aircraft or other obstacles "inthe intended line of approach it'otthe airfield. "For example, referringto Fig. 'Zfifthe pilot of the airplane l8 desiresito make 'a'ilanding watsa landing fieldlocated at the 'poin'till, the p lot 'llnows that such -a landing "can "safely" be in-aide if anotheraircraftis .Ylocate'd at the. point Z3'f-but not another aircraft is 'flocated "below The elimination of ground refi 'ectionsmakes' it possibletfor the rpilotof the airplane-18 to obtain 11 dic'at'ion off an bbstacleat, theipo;int"'93 with- ;ou bliteration 'of the ind'i'cation by the ground e'r'efnce z'smigxn.

"e elimination of ground reflections from'i'the alrneidj't ueseendiawng a 'moregra'duarslope, that is'fto""reducealtitudea greaterdistance'rrom landing fildfihan "would otherwise "be "posnly soil the presence of other aircraft but "also'en blesa-fiilotwhen approaching H in'viewof'th "dangeroffstrikingtall'chimineys', water towery and *the like; whichmay be ""tenn-i-nal of said third: and fourth controli'devices ground, when fit is pointed toward the ground. will maintain the :efiectivenessof the auto ranging equipment for eliminating :ground or surface reflections. This will :be true even .in the case of 5 rollingiground and areas with gradually .varying slopes whereas sharp obstructions such as cliffs edges of canyons and upwardly protruding sobstacles suchasitowers will represent discontinuities and roduce indications on the screen121l 1:0 "The characteristic .of :my ground-reflectionlimination apparatus make :obstacles standout more clearly-on theuscreenzi and prevent :rclatwely'v smooth or 'igently;rolling ;groundrepr.esenting a rgood tlanding surface :from;pi:oduc'in g1 oblit- 1'5 crating indications. As many changes could he made in :the :above construction *andmany apparently iwide'ly different embodiments :of this invention :could be made without departing from the a scope thereof. it is intended thatsall matter contained: in ithe abovedescription or .showniin .the accompanying drawings :shall ':be "interpteted .ias illustratlve notfini-alimiting sense.

What is claimed is: J I H 2-5 :1. Object locator circuits comprising .a coincidence circuit having a pentagrid convertcr tiibe having an anode, a cathode and i-first, .fsecond,

third, i'fourth and fi 'fth icontrol zelectro'des; ,first input coupling means :connected Lto said-first'con- 30, tr'ol electrodezforssupplying asreceiver inputi-sig;

connected for :applying anode-cathode current .:to asaid tube and controlled .lby signals :supplied 'from :-said rfirst and second input couplingmeans rand lex-tinguishableiby either of them, meansxonne'cted zto isa'id "energy zsupply' means "for :maintainingtsaid secondiand'rourthcontrol electrodes latxaliisubstantially constant :potential for shieldaing said third control selectrodeifrom "the gathers. :and :means also, connected :tosnid energy supply means for maintaining said'fifth zcontnolaelc e --trode at substantially .1cathodezliofiential.

. J2. Objectllocator circuitsrcomprisin acoinek :Idenceteircuit :having :principal signal -pu-t :ter-

. -mina'lsr'for supplying ia;principalzsig-nal, i'fiIEStflIld second:comparison1-signalinputzterminalfinmeans ior :esupplyin eto -::said com arison ,csienal' atelanimals signals "which are .di'sn ac dtin t me rela- Etion :hut substantially :contiguous, ants-t .dcuble :in put electric control .adevie" 0.1" :the typ shaving single 1 output "and two independent control 2 16:-

1ments, either of I which is independently capable :DI :extinguishingqcurrenti-n the control rdevice a wsecond,;double input; electric controldeviceaof :the -.timehaving a Z-singleioutput rand two independent .-;control elements, either of "which .--is ;-indep endently .capablepf --,extinguishing current in th control device, {one of said-:control p.elements.of ..eac= h ,of saidrcontrolz-devices rbeingcoup-led .tosaid princ-ipal signal input fterminaLlthe otherof said -.contr,ol elements rat-said {first :device being cousgpled gtov saidlfirst comparison signal input {ter- ,minal and the..-- other of .-said control ;element s,.of the second ,electricicontrol device "beingflcoupled to the second comparison signal .input terx'ninal, third .and vfourth .electric .control..,devices co nnectedein' series, having av iunction terminal and e c ,having .a .cr'mtrol element, .coupling means betweenthe control element of, the third control jfdevice and the output ofsaidtfirst' controlidevice, andicoup'ling ,means between said fourth control device "and the "output "of "said second; control device, "whereby vthe -'-1: otentialof the -Junction varies in accordance with variation in time of occurrence of a signal applied to said principal signal input terminals in relation to the signals at said comparison signal input terminals.

3. Object locator circuits comprising a coincidence circuit having principal signal input terminals for supplying a principal signal, first and second comparison ignal input terminals, means for supplying to said comparison signal terminals signals which are displaced in time relation but substantially contiguous, a first double input electric control device of the type having asingle output and two independent control elements, either of which is independently capable of extinguishing current in the control device, a second double input electric control device of the type having a single output and two independent control elements, either of which is independently capable of extinguishing current in the control device, one of said control elements of 7 each of said control devices being coupled to said principal signal input terminal, the other of said control elements of said first device being coupled to said first comparison signal input terminal, and the other of said control elements of the second electric control device being coupled to the second comparison signal input terminal, a first low time constant peak voltmeter responsive to the first electric control device, a second low time constant peak voltmeter responsive to the second electric control device, and means for comparing the magnitudes of indications of said low time constant peak voltmeters.

4. Object locator circuits comprising a square wave generator for producing a wave having abrupt termination, a generator for producing a range gate initiated by the termination of said first-mentioned square wave, a generator for producing a second range gate initiated by the termination of said first range gate, input signal terminals, and means'independently responsive to two diiTerent inputs for comparing coincidence of signals applied to said input terminals with waves supplied by said first and second range gate generators.

5. Object locator circuits comprising a signal coincidence circuit'having first and second comparison signal input terminals with means for supplying thereto comparison signals displaced in time relation but substantially contiguous,

principal signal input terminals for reception of a signal to be compared in time relation with said comparison signals, a pair of electric control devices each having a pair of control elements, one of said control elements of each of said electric control devices being coup-led to said principal signal input terminal and the remaining control elements of said electric control devices each being coupled to a different one of said comparison signal input terminals, means responsive to said electric control devices for producing a potential varying from a normal value in accordance with variations in time relation with respect to said comparison signals of a signal which may be supplied to said principal signal input terminal, and a cathode follower electronic stage having a control element, coupling means between said variable potential means and said control element, and high resistance means for positively biasing the control element of said cathode follower stage for causing the output thereof to drift to a maximum in the event of failure of signal input to said principal signal input terminal.

6. Object locator circuits comprising a signal coincidence circuit having first and second comparison signal input terminals with means for supplying thereto comparison signals displaced in time relation but substantially contiguous, a principal signal input terminal for reception of a signal to be compared in time relation with said comparison signals, a pair of electric control devices each having a pair of control elements, one of said control elements of each of said electric control devices being coupled to said principal signal input terminal and the remaining control elements of said electric control devices each being coupled to a difierent one of said comparison signal input terminals, means responsive to said electric control devices for producing a potential varying from an average value in accordance with variations in time relation with respect to said comparison signals of a signal which may be supplied to said principal signal input terminal, and means for biasing said potential varying means to produce drift to maximum output in the event of failure of signal input to said principal signal input terminal.

7. Object locator circuits comprising a signal coincidence circuit having first and second cornparison signal input terminals with means for supplying thereto com-parison signal displaced in time relation but substantially contiguous, a principal signal input terminal for reception of a signal to be compared in time relation with said comparison signals, a pair of electric control devices each having a pair of high-impedance input control elements, one of said control elements of each of said electric control devices being coupled to said principal signal input terminal and the remaining control elements of said electric control devices each being coupled to a different one of said comparison signal input terminals, and means for comparing the outputs of said electric control devices.

8. Object locator circuits comprising a signal coincidence circuit having a pair of coincidence devices with input terminals for receiving asignal and input terminals for receiving time displaced range gates, said coincidence devices having anode circuits and phase inversion transformers connected thereto, and a pair of peak voltmeters, each of said voltmeters being coupled,

to one of said coincidence devices.

9. Object locator circuits comprising a pair of pulse generators for producing two time displaced substantially contiguous range gates, means for rounding the end of the first range gate and the front of the second, a coincidence comparison circuit jointly responsive to said range gates and an input signal, and means responsive to said latter circuit for producing an output varying with the relative degrees of coincidence of said range gates with the signal input to said input comparison circuit.

ROBERT F. MOZLEY.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,895,774 Smets et a1 Jan. 31, 1933 2,178,340 Geiger Oct. 31, 1939 2,200,130 Lewis et al. May 7, 1940 2,221,517 Holters Nov. 12, 1940 2,333,605 Watson Nov. 2, 1943 2,403,429 Anderson July 9, 1946 

